SUBUNIT ORGANIZATION AND STRUCTURE OF LON PROTEASE

扫描透射电子显微镜 (STEM) 已用于确定 ATP 依赖性蛋白酶 Lon 的亚基组织。这种酶在降解原核生物以及真核生物线粒体中的错误折叠蛋白质方面发挥着重要作用。 Lon 由单个多肽链的多个拷贝组成，其中包含 ATP 酶 (A) 和蛋白酶 (P) 结构域。细菌Lon的序列与真核生物Lon具有很强的同源性，据报道真核生物Lon可形成七聚环。然而，对于细菌Lon，目前公布的数据尚无定论。暗场 STEM 测量表明，全长大肠杆菌 Lon（野生型和 Ser-ala 突变体）以及 Lon-NA 由十二聚体组成，而 Lon-AP 则形成六聚体。通过与作为 ClpAP 蛋白酶复合物的 ATP 酶成分的蛋白质 ClpA 类比，Lon 很可能由两个六聚环组成。 Lon-AP 仅形成六聚体的事实表明，全酶中两个六聚体环的缔合可能需要 N 末端结构域。 - 扫描透射电子显微镜、lon蛋白酶、亚基组织、结构、分子量

Scanning transmission electron microscopy (STEM) has been applied to determine the subunit organization of the ATP-dependent protease, Lon. This enzyme plays an important role in degrading misfolded proteins in prokaryotes as well as in the mitochrondria of eukaryotes. Lon consists of multiple copies of a single polypeptide chain that contains both the ATPase (A) and protease (P) domains. The sequence of bacterial Lon has a strong homology with eukaryotic Lon which has been reported to form heptameric rings. However, for bacterial Lon, currently published data are inconclusive. Dark-field STEM measurements show that full-length E. coli Lon (wild type and a ser-ala mutant) as well as Lon-NA are composed of dodecamers, whereas Lon-AP forms hexamers. By analogy with the protein ClpA which is the ATPase component of the ClpAP protease complex, it is likely that Lon is comprised of two hexameric rings. The fact that Lon-AP only forms hexamers suggests that the N-terminal domain may be required for association of two hexameric rings in the holoenzyme. - Scanning transmission electron microscopy, lon protease, subunit organization, structure, molecular weight